There exist several electrochemical devices for determining the concentration of various biologically important gases on biological surfaces. Because of the critical role that oxygen plays in physiological events, most of these instruments primarily monitor oxygen, and particularly are employed to monitor oxygen concentrations in patients suffering from disease. The principle on which the instruments operate is that of the common oxygen electrode as described by L. C. Clark, Jr., in Transactions American Society Artificial Internal Organs (1956, 2:41). While there exist a number of oxygen sensors suitable for monitoring oxygen at or on such biological surfaces as tissues, organs, blood vessels, etc., none are capable of accurately determining oxygen at different specific locations on the surface. The reasons are two-fold: First, the sensors have not been satisfactorily designed with multiple independent sensing capacity capable of close physical contact with the surface. The latter is required for determining oxygen across nonuniform shaped surfaces. Second, it is difficult to precisely position existing sensors over the diminutive biological structures, particularly superficial blood vessels where it is often desirable to determine the oxygen contour profile across the vessel surface, because it is difficult to visually ascertain where on the surface the electrodes are located.